The specificity of an antibody is due to

Correct Answer: D

Rationale: Variable regions determine specificity; valence is binding capacity, Fc is effector.

Correct Answer: B

Rationale: A hallmark of the adaptive immune system is that it progressively alters its response upon reexposure to an antigenic stimulus, and in doing so, it must recall the previous exposure, a process known as memory. Although they are members of the innate immune system and do not possess immunologic memory, phagocytes may be influenced by the adaptive immune system. Consistency in immune response from initial to subsequent encounters is a hallmark of the innate immune response. Immunologic memory of the adaptive immune system is not passed genetically from one generation of individuals to the next. Detection of diminished MHC class I expression is a function of natural killer cells, members of the innate immune system.

Correct Answer: B

Rationale: The primary response has a longer lag phase (days) before antibody production, unlike the faster, stronger secondary response.

Correct Answer: C

Rationale: Lymph flows from afferent lymphatics into the node, then exits via efferent lymphatics, draining infection sites.

Correct Answer: D

Rationale: Helper T cells release lymphokines like cytokines; not histamines or antibodies .